<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      * {
        margin: 0;
        padding: 0;
        box-sizing: border-box;
      }
      header,
      footer {
        height: 50px;
        background-color: salmon;
      }
      body {
        height: 100vh;
      }
      .main {
        height: calc(100vh - 100px);
        background-color: seagreen;
        display: flex;
      }
      .left {
        width: 100px;
        background-color: skyblue;
        overflow: auto;
      }
    </style>
  </head>
  <body>
    <header>1</header>
    <div class="main">
      <div class="left">2</div>
      <div class="right">3</div>
    </div>
    <footer>4</footer>
  </body>
</html>
